Not Applicable
The present invention relates generally to detecting the orientation of a body. More particularly, the present invention relates to alignment apparatuses and methods for determining whether leads on a semiconductor package are aligned in a predetermined alignment prior to placement on and attachment to a substrate. The invention can be generally used in conjunction with or integral to pick and place machines, such as surface mount placement machines, die attach machines, tape and reel production machines, wire bond machines, and the like, to verify proper lead alignment on components being placed by the machines.
Solid state electrical devices are typically produced by attaching a plurality of miniaturized electrical components to a common substrate, such as a printed circuit board. The proper performance of the device is dependent upon the precise placement of each electrical component on the substrate.
The placement of electrical components on a substrate is commonly performed using machines generally known as pick and place machines. Pick and place machines typically employ a number of movable heads each having a nozzle through which a negative pressure, preferably a vacuum, is applied to pick a component from a feed source, such as a continuous tape and reel assembly. The pick and place machine controls the movement of each head to precisely place the components on a substrate, after which the vacuum or suction is released.
Commonly, pick and place machines incorporate sensor systems that detect whether a component is properly aligned in a predetermined angular orientation prior to placing. Examples of such systems are discussed in U.S. Pat. Nos. 5,040,291 issued to Janisiewicz (xe2x80x9c""291 patentxe2x80x9d) and 5,377,405 issued to Sakurai et al.
Other placement systems ensure alignment of the component by providing either a recessed surface in a substrate shaped to receive the component or mating surfaces on the component and the substrate. For example, See U.S. Pat. No. 5,034,802 issued to Liebes, et al. (the xe2x80x9c""802 patentxe2x80x9d). The ""802 patent also discloses the use of an alignment jig for aligning a component prior to picking and placing the component on the substrate. The alignment jigs employ large recesses that are tapered down to the dimensions of the component. The large tapered recess allows the components to be placed less precisely in the jig. The taper on the jig then serves to essentially xe2x80x9cfunnelxe2x80x9d the components into a precise alignment.
A problem exists with the aforementioned alignment methods when used with traditional rectangular shaped components having leads extending from two opposing sides. If the component is 180xc2x0 out of alignment, the leads will appear to be properly aligned using the above methods. A component that has its leads attached 180xc2x0 out of alignment will generally function improperly at a minimum and may result in damage to the component and/or other components connected to the component. The obvious exception is a component that is designed to employ mirror image lead connections, which is not the typical design.
This problem is further complicated by components that are designed to have symmetric leads on more than two sides, such as a square shaped component. A 90xc2x0 rotation of a square shaped component in the plane of the leads will result in a lead misalignment that is undetectable using prior art methods.
The misalignment of leads on aligned components is a defective condition that is presently not detectable using general component orientation systems of the prior art. Thus, the present invention is directed to detecting the misalignment of lead components irrespective of the general orientation of the component to provide apparatuses and methods that can be used to determine the lead alignment of components prior to placement on and attachment to a substrate.
The above objectives and others are accomplished by methods and apparatuses in accordance with the present invention. A method of the present invention contemplates placing a component having leads to a substrate by providing a fiducial marker on a component to be placed on a substrate that uniquely distinguishes the alignment of leads on the component. The alignment of the fiducial marker on the component is detected and compared to a predetermined fiducial alignment corresponding to a predetermined lead alignment. The component is placed on the substrate when the detected fiducial alignment corresponds to the predetermined fiducial alignment. In addition, a component that has misaligned leads can be discarded or the alignment of the components can be properly realigned in accordance with an alignment offset.
Apparatuses of the present invention can be operated in conjunction with or integral to various pick and place machines, such as surface mount placement machines, die attach machines, tape and reel production machines, and wire bond machines. Generally, the apparatus includes a nest for receiving a component and detector positioned to detect whether leads on the component in the nest are properly aligned and provide a signal indicative of the alignment. In a preferred embodiment, a physically asymmetric fiducial marker is provided on the component and a correspondingly asymmetric recess in provide in a surface of the nest. The detector is positioned to detect whether the asymmetric portions of the component and the nest mate. In another embodiment, a receiver is positioned in a pick and place machine relative to the feed source to detect the alignment of the leads on a component prior to the component being fed to a pick station for placement on a substrate.
Accordingly, the present invention overcomes the aforementioned problems to provide apparatuses and methods that provide the ability to determine, verify, and/or correct the alignment of leads on components prior to placing the components on a substrate. These advantages and others will become apparent from the following detailed description.